Remove start & end from range options

[vweevers]

I propose that we remove the start and end options from iterators & streams. Without doing a soft deprecation, because they were documented as legacy options 5 years ago. I prefer ripping off the band aid and throwing an error if start or end properties are present in options.

@Level/core Anyone opposed? Give a thumbs up or down. Keep reading for the motivation.

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The start/end options are more surprising in reverse mode. While ltgte options fulfill the documented promise of "the returned entries are the same, but in reverse", start/end options must be swapped by the user to achieve that.

The relevant code to handle the whole set of options - which I think in many implementations has been built up through trial & error, putting trust in the extensive tests - is hard to follow, and hard to change.

In addition, there are rules of precedence between start/end and ltgte although a formal decision was never made (Level/abstract-leveldown#70) and tests don't cover it.

[juliangruber]

I would still favor a soft deprecation, so we don't surprise anyone, but if you want to go ahead and remove it right away that should work too I guess

[vweevers]

@juliangruber It'll be released as semver-major across the board, with the usual changelogs and upgrade guides. For the folks that missed both the 5-year-long documented notice and the upgrade guides, we'll throw an error. I think that's more than enough.

[ralphtheninja]

This will greatly simplify the leveldown C++ code.

[vweevers]

Work is tracked in #98.